This invention relates to microcontrollers and, in particular, to microcontrollers for use in battery management applications and having an on-chip temperature sensor for monitoring the temperature of a battery pack of which the microcontroller is included therein.
Microcontrollers include a microprocessor core as well as timer circuits and ROM and RAM memory all of which are embedded on a single semiconductor integrated circuit (IC). Microcontrollers are used in a wide diversity of present day application with new applications found almost daily. In hand held instruments such as tiny pocket-sized pagers, the microcontroller is responsive to received characters to interpret them, produce a beep to notify the user of an incoming message, and produce multiple messages suitable for display, for example, on a liquid crystal display (LCD). Microcontrollers are also used for controlling keyboards for personal computers, in which the microcontroller serves to offload many tasks formally handled by the processor. Additionally, microcontrollers are also used in modems for command interpretation and data transmission, in printer buffers for high speed dumping of data in preparation for driving the printer at considerable lower speed at which the printer operates or for color plotters, in color copiers, electronic typewriters, cable television terminal equipment, lawn sprinkling controls, credit card phone equipment, automotive applications such as engine control modules, antilock braking systems, automobile suspension control for desired destination of ride softness or rigidity depending upon user preference, and a host of other applications used daily by industrial and consumer customers.
Microcontrollers may also be used for monitoring and controlling a battery. Such an application is becoming increasingly important because many electronic devices are portable and require the use of a battery for its power source. However, for adequate fast-charge termination as well as accurate fuel gauging, it is important to know the temperature of the battery pack. Accordingly, it would be desirable to provide a temperature sensor for monitoring the temperature of the battery pack.
A variety of temperature sensors are well known in the art. However, standard devices such as thermocouples, thermistors or resistance temperature devices all have limitations which prevent them from being easily or widely used. For example, thermocouples require accurate cold junction compensation, some form of linearization, and produce a low level voltage output which is subject to electrical noise interference. Thermistors and resistance temperature devices have a non-linear characteristic which requires careful compensation and a wide dynamic electrical range. In addition, making a good resistance measurement demands an accurate voltage source, low level precision current sensing, and careful lead compensation.
Referring to U.S. Pat. No. (U.S. Pat. No.) 3,940,760 to Brokaw (the '760 patent), a temperature sensor device is disclosed that makes use of the linear base-to-emitter voltage versus temperature property of a transistor. Such an approach may be implemented by a device that uses first and second transistors operated at a constant ratio of emitter current densities and having their bases inter-connected whereby the difference between their base-emitter voltages appear across a resistor coupled in series with the emitter of one of the transistors. The difference voltage (V.sub.T) appearing across the resistor may be expressed as: V.sub.T =(KT/q).times.Ln[Je1/Je2], where q is the charge of an electron, in coulombs, K is Boltzman's constant, T is absolute temperature in degrees Kelvin, and Je1 and Je2 are the current densities for the first and second transistors, respectively. While such a device provides basic temperature sensing, it is not useful for extremely accurate temperature sensing, especially over wide temperature ranges.
Referring now to U.S. Pat. No. 4,123,698 to Timko, an improved temperature sensing device that makes use of the device described in the '760 patent is disclosed. The sensor disclosed in Timko attempts to improve the accuracy and extend the temperature range of the overall temperature sensor while not causing bias current or substrate leakage current errors, which as mentioned in Timko, was a problem with the device of the '760 patent. However, such a sensor requires additional components for implementation and may not be suitable for on-chip fabrication with a microcontroller.
It is therefor an object of the present invention to provide an improved on-chip temperature sensor tot use with a microcontroller for monitoring the temperature of the microcontroller as well as a battery pack of which the microcontroller and a battery, to be monitored and controlled, is housed within.